<!DOCTYPE html>
<html>
    <head>
        <meta charset=utf-8>
    </head>
    <body>
    	<ul>
            <li>.</li>
            <li>.</li>
            <li>.</li>
        </ul>

        <script type="text/javascript">
            // 补全代码
            document.getElementsByTagName('ul')[0].onclick=(el)=>{
                el.target.innerText='..'
            }
        </script>
    </body>
</html>